Study On Elliptic Bandpass Filters Constructed On Multilayer Substrates

Microwave filter is one of the elements which are most widely used in communication systems.There are two kinds of circuits for microwave filters: one is composed of distributed-elements and the other is composed of lumped-elements.The filter realized by distributed-elements has an excellent performance but its size is relatively large.Meanwhile,the performance of the filter realized by lumped-elements is poor but its size is very small.Miniaturization and high-performance are always the goal in microwave filters design.The filter design by multilayer substrate has both high performance and small size.However,the design of this filter is very complex due to the parasitic inductors and capacitors,so there is still a long way to go.The elliptic filter has a good performance,so it is always used to design the circuit of the microwave filter.Especially when using multilayer substrates to design filters of lumped-elements,the inductors and capacitors of the elliptic filter usually appear in pairs,which can reduce the parasitic inductors and capacitors.The study of this paper is on the filter of lumped-elements,the main work and innovation are as follows:(1)By Analyzing elements designed by multilayer substrates,especially the advantages and disadvantages of capacitors realized by multilayer substrates,some new capacitors are designed.By tested by an electromagnetic simulation software named ADS,the new capacitor is proved to have a higher resonance frequency and the parasitic capacitors and inductors are addressed well.(2)According to the circuit model of the filter,a new physical model of the elliptic-function bandpass filter is proposed and created.This model has seven layers,its structure is compact and the layout is reasonable.According to the laws and knowledge of the filter,a solution can be found to reduce the parasitic influence.By doing this,the performance of the filter can be improved a lot.At last,the model is sent to the factory to be created.The result processed by ADS and the result of the physical model are well measured,which shows that the design of this filter meets the requirement and the filter has an excellent performance.